[Article]Multimodal warning signals for a multiple predator world

Nature 455, 96-99 (4 September 2008) | doi:10.1038/nature07087; Received 10 February 2008; Accepted 14 May 2008

Multimodal warning signals for a multiple predator world

John M. Ratcliffe^1,3 & Marie L. Nydam^2,3

1. Center for Sound Communication, Institute of Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
2. Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA
3. These authors contributed equally to this work.

Correspondence to: John M. Ratcliffe^1,3Marie L. Nydam^2,3 Correspondence and requests for materials should be addressed to M.L.N. (Email: mln32@cornell.edu) or J.M.R. (Email: jmr@biology.sdu.dk).

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Abstract

Aposematism is an anti-predator defence, dependent on a predator's ability to associate unprofitable prey with a prey-borne signal¹. Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated^{2, 3}. Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats—predators with divergent sensory capacities. Many tiger moths advertise chemical defence^{4, 5} using conspicuous colouration and/or ultrasonic clicks^{3, 6}. During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.